ABSTRACT: In this exploratory application, two senior investigators with complementary expertise in tumor immunology and circadian rhythm biology propose to test a novel answer to ?Provocative Question #6: How do circadian processes affect tumor development, progression and response to therapy? We propose the existence of a previously unexplored link between circadian rhythms and anti-tumor immune function, such that disruption of circadian processes increases homeostatic stresses leading to increased circulating catecholamine (norepinephrine) levels. In turn, the resultant increased ?-adrenergic receptor signaling in the tumor microenvironment will 1) subvert on-going anti-tumor immune activity, particularly that of CD8+ T cells and 2) reduce responsiveness to checkpoint inhibitor immunotherapy. Although this application is exploratory in nature, it has a strong Scientific Premise since our recent findings in mouse models demonstrate that the degree of adrenergic stress activity by the sympathetic nervous system, (already known to be influenced by circadian processes) plays a profound role in regulating immune control of tumors, including even carcinogen- induced tumors, as well as the efficacy of anti-PD-1 checkpoint inhibitor antibodies. Now we will test, for the first time, the hypothesis that adrenergic-stress mediated control of anti-tumor immunity is influenced by circadian disruption using higly relevant models of sleep disruption similar to those of humans affected by ?shift work? or ?jet lag.? We will address this hypothesis in two aims using well characterized murine models of circadian disruption and tumor growth/immunotherapy already in place in the laboratories of the co-PIs. Aim 1 will test whether circadian disruption by ?shift work? or ?jet-lag? light/dark models accelerates tumor progression, and subverts anti-tumor immune activity, particularly that of CD8+ T cells (in which preliminary data reveals significantly impaired metabolic programming in response to adrenergic signaling.) Aim 2 will test whether circadian disruption influences the response to checkpoint inhibitor immunotherapy using anti-PD-1 antibodies. These studies are predicted to identify, for the first time, the impact of circadian disruption on the immune contexture of tumors and particularly, on ?-adrenergic receptor signaling- induced suppression of CD8+ T cells. If successful, our studies will clarify a new mechanism-based understanding of how disrupted circadian processes can lead to increased tumor formation and growth and impaired response to therapies. Excitingly, these studies could also lead to new, and immediately feasible, therapeutic approaches for cancer patients (who often experience circadian rhythm disruption) that reduce adrenergic stress (e.g., by the use of common ?-blockers) to improve the efficacy of immunotherapy.